Musculoskeletal Pathophysiology - BONES Flashcards
What are the two divisions of bones?
- Axial Skeleton
- Appendicular Skeleton
(206 bones total)
What are the 2 main functions of bones and the skeleton?
- Mechanical functions
- support
- provide movement
- protection
- Physiological functions
- produce blood cells
- store minerals
What are the two types of bones?
1. Compact bone
- dense connective tissue
- white, smooth, solid
- makes up 80% of bone mass
2. Spongy bone
- internal
- appears porous
- internial cavity of this bone contains BM
- makes up 20% of bone mass
What are the four classifications of bone shape?
(Bones are classified according to shape and function)
- Long
- Short
- Flat
- Irregular
Long Bones
Length > width
Serve as rigid levers and used bu muscles to generate movement
e.g. humerous, femur, small bones in fingers & toes
Long bone structure
Short Bones
length ~ width
limited motion, glide across each other to alow bending in multiple directions (e.g. wrists and ankles)
e.g. carpals & tarsals
Flat bones
flat, thin surfaces, may be slightly curved
extensive surfaces for muscle attatchment
protect underlying tissue
e.g. cranial bones, ribs, sternum, scapula
Flat bone structure
Periosteum - outer membrane/layer of bone (outer part of Compact bone)
Diplöe - aka Spongy bone
Irregular bones
elaborat e shapr - do not fit anywhere else or under any other categories
e.g. vertebrae, some bones in the skull
Bone turnover
5-7% recycled weekly
0.5g in/out adult skeleton
Bones are continuously remodelled
- mineral deposition and resrption
- 2 major cell types involved
- osteoblasts → osteocytes
- osteoclasts
What are the two major cell types involved in bone remodelling?
- (osteogenic cell) → osteoblasts → osteocytes
- osteoblast:
- rough ER
- nucleus
- mitochondrion
- (stem cell) → fusion → osteoclast
- process: fusion
- ruffled border
- nuclei & lysosomes
Osteoclasts
Facilitate mineral resorption
- by dissolving crystals and releasing minerals into blood
- pump H+ out of cell
- Cl- follow by electrical attraction
- ECF HCl, pH 4.0
ECF = Extra Cellular Fluid
…
- found on surface of osseous tissue (howship’s lacunae)
- arrise by fusion of unnucleated stem cells or from fused monocytes
- osseous matrix facing osteoclast is demineralised → assumption: osteoclasts involved in resorption
- osteoclasts are NOT apparent when bone resorption activity ceases (e.g. following healing of a fracture)
Osteoblasts
- associated with bone formation (thus located wherer new bone is forming)
- cuboidal/pyramidal stratified
- contain enzyme: alkaline phosphatase used to calicfy the osseous tissue
Osteocytes
An osteoblast which has been enclosed within bony matrix space called the “lacuna”
Calcification
When osteoclasts do not dissolve crystals → hydroxyapatite crystal deposition → calcification
- tissues have inhibitors to prevent hydroxyapatite crystal deposition (calcification)
- lungs
- eyes
- brains
- tendons
- muscles
- arteries
Osserous tissue (bone tissue)
Rigid form of connective tissue which forms the skeleton
Three primary componenets
- Cells
- Osteoblasts
- Osteocytes
- Osteoclasts
- Osseous matrix (2 componenets)
- Organic component (osteocollagenous fibres)
- Inorganic componene (calcium phosphate crystals)
- Bone architecture
* shape/size/structure
Physiology of osseous tissue
Bones are metabolically active
- influences the rest of the body by exchanging minerals with tissue fluid
- 99% Ca stored in bones
- 1% stored in blood & tissue
What is the normal blood (plasma) Calcium level?
9.2 - 10.4 mg/dL
Calcium homeostatis
Depends on balance b/w:
- diatary intake (~1000mg/day)
- urinary & fecal loss (650 & 350mg/day)
- exchange b/w osseous bone tissue
Regulated by 3 hormones:
- Calcitriol
- Calcitonin
- Parathyroid hormone
Calcitriol is also known as:
Activated Vitamin D
Behaves like a hormone
Produced by sequential action of skin, liver, kidneys:
7-dehydrocholestrol → UV + skin → VD3 /cholecalciferol → liver → calcidiol → kidney → calcitriol
Vitamin D deficiency
Abnormal softness of bones
Rickets in children
- Bowed legs & pelvis deformalities
- Common skull and ribcage
- Epiphyseal plates cannot be calcified → continue to widen & end of long bones visibly enlarged and abnormally long
Osteomalacia in adults
- Bones are inadequately mineralised
- Little deposition of calcium crystals
- Symptom: pain when weight put on affected bones
Calcitonin
Secreted by clear cells (C cells) in Thyroid gland when calcium levels rise
Calcitonin: Correction of hypercalcemia
Remember Calcitonin is secreted by C-cells in the thyroid in response to increases in calcium level aka hypercalcemia…
↑Ca2+ ⇒ Calcitronin secretion ⇒ ↓osteoclast activity ⇒ ↓bone resorption ⇒ ↓Ca2+
↑Ca2+ ⇒ Calcitronin secretion ⇒ ↑osteoblast activity⇒ ↑bone deposition ⇒ ↓Ca2+
Roles of Calcitonin
Important role in children where osteoclasts liberate 5g of Ca from bone ⇒ blood, daily
Weak effect in most adults where osteoclasts liberate only 0.8g of calcium into blood, daily
- Calcitonin not shown to cause any adult diesases
- may prevent bone loss in women during pregnancy and lactation
Parathyroid Hormone (PTH)
Released by parathyroid glands at posterior of thyroid gland when blood calcium is low
- A 1% drop in blood calcium doubles the secretion of PTH!
Hypoparathyroidism
Causes rapid decline in blood Ca levels
leads to fatal tetany in 3-4 days
Hyperparathyroidism
- Leads to excess PTH secretion
- Usually casued by PT tumour
- Causes soft bones, deformed and fragile
- Raises blood Ca and Phospate
- Promotes formation of kidney stones composed of Calcium phosphate
Hypocalcemia
Blood Ca deficiency
- ↑excitability of nervous system
- muscle tremors/spasms/cramps (tetany)
- begins when Ca falls ~ 6mg/dL
- at 4mg/dL larynx muscles contracy (laryngospasm) → suffocation
Vitamin D deficeiency
Diarrhea
Thyroid tumours
Uneractive parathyroid glands
Pregnanacy and lactation
#1 cause: accidental removal of parathyroid glands during thruoid surgery → tetany within 4 days if no HRT given
Hypercalcemia
Blood Ca excess
- At 12mg/dL and higher → depression of nervous system, emotional disturbances, muscle weakness, sluggish reflexed, cariac arrest
Causes rapid decline in blood Ca levels
leads to fatal tetany in 3-4 days
Osteoporosis
- Most common bone disease
- “Porous bones”
- Severe loss of bone density
- Fractures can occur
- Hip
- Wrist
- Vertebral column
- Kyphosis (widows hump)
Risk factors for Osteoporosis
Postmenopausal anglo/white women at greatest risk
- start out with rel. less bone density
- start losing it earlier (~35)
- lose bone density more rapidly
Estrogen and Osteoporosis
Estrogen:
- Maintains bone density (by:)
- inhibits osteoclast activity
Meopause-ovaries stop secreting estrogen → ↑ osteoclast activity and outpaces osteoblast activity
- Treatment: Estrogen Replacement Therapy (ERT)
Other risk factors for osteoporosis
- 20% of men have ↓ estrogen levels
- smoking
- alcohol
- diabetes mellitus
- poor diet
- little weight-bearing exercise
- low body fat
How can osteoporosis be diagnosed and how is it prevented?
Diagnosis:
- DEXA (Bone density scan / bone densiometry)
- Dual Energy X-ray Absorptiometry
Prevention:
- Calcium
- Fluoridated water
- ↓ Carbonated beverages
- Weight bearing exercise
Paget’s Disease
A chronic condition which casues abnormal enlargment and weakening of the bones
- affects spine, pelvis, femur, skull
- increses in deformity and pain
- rare before 40
- common in Aus, NZ, GB, US
- Drug therapies can prevent bone breakdown
Osteomelitis
A bone marrow infection caused by bacteria or other germs
- Often children
- Inflammation/infection of bone & BM
- Usually in long bones of arms and legs
- (or bone around knee, hip, or ankle)
Sypmtoms:
- Swelling and pain on movement
Treatment:
- Antibiotic therapy
- Chronic conditions → surgery
Sciatica
Sciatica is pain in the buttock and leg, extending beyond the knee, caused by pressure on nerves in the lower back. Can be triggered by slipped vertebral discs, pinched nerves or some arthritese.
- Age related: ~50% of people >60
- Compression of tibial & common peroneal nerves, together → sciatic nerve (ischiatic nerve)
- Associated with muscle spasms in paravertebral and hamstring muscles
Most common Causes:
- Intervertebral disk protrusion (herniation)
- Bone irregularity in vertebra
- Spinal tumour
Treatment:
- Relieving muscle spasms with
- bed rest
- local warmth
- massage
- oil analgesics
- NSAIDs
- oral muscular relaxants
- Surgery
- Laminectomy: removal of part of vertebral arch to allow for more room for disk protusion
- Spinal fusion of 2 vertebrae by removing the herniated disk
What are two types of bone fractures and their causes?
1.Stress fracture
- Break by abnormal bone trauma
- falls
- athletics
- military combat
2. Pathological fracture
- Break in bone weakened by other disease
- Stress that would not break healthy bones
- (Secondary ?)
- bone cancer
- osteoporosis
Types of bone fractures
Also Nondisplaced: fully broken but in original position
Healing of fractures
1. Hematoma formation
The hematoma is converted to granulation tissue by invasino of cells and blood capilaries
2. Soft callus formation
Deporsition of collagen and fibrocartilage converts granulation tissue to soft callus
3. Hard callus formation
Osteoblasts deposit a temporary bony collar around the fracture to unite the broken pieces while ossification occurs
4. Bone remodelling
Small bone fragments are removed by osteoclasts, while osteoblasts deposit spongy bone and then convert it to compact bone
